Method of making target electrode for barrier storage grid tube



C. L. DAY

METHOD OF MAKING TARGET ELECTRODE FOR BARRIER STORAGE GRID TUBE Filed June 28, 1957 )l @liv fnl/antan Cyr/YL. Davy, b (Quoi @QQ/21% 'y Mtl-ornqys.

United States Patent Office 3,92%,622 Patented Feb. 13, 1962 3,020,622 METHGD F MAKING TARGET ELECTRODE FR BARRIER STORAGE GRID TUBE Cyril L. Day, Huntington, lud., assignor to International Telephone and Telegraph Corporation Filed .lune 23, i957, Ser. No. 66S,671 4 Claims. (Cl. 2925.18)

This invention relates to barrier grid storage tubes and more particularly to the target electrode assemblies incorporated in such tubes and to the method of making such target electrode assemblies.

Barrier grid storage tubes are now commonly used in such devices as computers, being employed in binary computers for storing and reading-out yes-no answers, and in a number of radar applications. These tubes, which are of the cathode ray type, are Well-known in the art, as shown for example in Patent No. 2,538,836 of January 23, 1951, to A. S. Jensen. Such tubes conventionally include an electron gun assembly including a cathode heated by a suitable lament, a control grid and an accelerating anode, positioned within an elongated envelope at one end thereof. Suitable deflecting and focusing elements are conventionally provided for causing the electron beam produced by the electron gun to scan a target electrode assembly positioned within the envelope at the other end thereof. The target electrode assembly comprises a grid or screen arranged on one side of the dielectric sheet and a metal plate arranged on the other.

The electron beam from the electron gun is caused to scan the target electrode assembly providing secondary emission greater than unity. Each square of the target electrode formed by the screen or grid in essence forms a separate capacitor with the metal backing plate and thus may be charged positively or negatively by the electron beam depending upon the polarity of the input signal applied to the metal plate and screen of the target assembly. These charges may subsequently be taken olf of the target electrode assembly by a subsequent scanning by the electron beam.

In prior barrier grid storage tubes known to the applicant, the target electrode has Ibeen flat. Barrier grid storage tubes having such flat target electrodes have been restricted in resolution, i.e., the number of bits of information stored for the diameter of the target, since it is ,by increasing the diameter of the target since it becomes increasingly difficult to collimate, i.e., focus, the beam. It is important, however, particularly in computers, that -good resolution be provided in barrier grid storage tubes and further that there be a minimum of overlapping or cross-talk in reading-out the bits of information stored on the target. In order to decrease cross-talk, however, while retaining the same number of bits of information stored, i.e., the same resolution, or to increase the number of bits of information capable of storage by the target and'thus increasing the resolution without increasing the crosstalk, it is necessary to increase the size of the target electrode or to decrease the size of the electron beam. However, as indicated above, the advantage to be gained by increasing the target diameter is limited as is the gain by decreasing the beam size. Furthermore, shading is introduced as the target diameter increases because the grid fstructure has appreciable thickness and thus there is a tendency in storage tubes having flat targets for the elec- ;in FIG. 1.

tron beam to be shaded by the thickness of the grid toward the edges of Ythe target since the beam does not have normal incidence to the target except adjacent the center; any increase in the size of the target in an effort to decrease cross-talk or increase resolution by increasing the number of bits stored increases the shading effect adjacent the edges of the target. Furthermore, with flat target electrodes, the beam is most accurately focused only at the center of the target and is increasingly olf focus as the outer edge of the target is approached; this also tends to increase cross-talk when the beam scans areas of the target adjacent the outer edges.

I have found that the above-mentioned disadvantages inherent in storage tubes having ilat storage electrodes are substantially eliminated by providing a bowl-shaped or spherical target electrode preferably having the locus of its radius of curvature located approximately at the center of deflection of the electron beam. With such a bowlshaped target electrode, the electron beam has normal incidence at all points on the target and thus the shading yimproved method of making a target electrode for a barrier grid storage tube.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein- In the drawings: Y

FIG. 1 is a schematic view of a barrier grid storage tube incorporating a conventional flat target electrode;

FIG. 2 is a schematic view similar to FIG. l but illustrating a barrier grid storage tube incorporating my improved bowl-shaped target electrode; and

FIG. 3 is a view in cross-section of an actual barrier grid storage tube incorporating the improved target electrode of my invention.

Referring now to FIG. 1, there is shown in simplified form with non-essential details eliminated a prior art barrier grid storage tube 1 having an enclosing envelope 2 with a conventional electron gun assembly 3 located at end 4 of envelope 2 and with a conventional at target electrode assembly 5 located at the other end 6 of the envelope 2. For purposes of explanation, the compo- .nents of the target electrode 5 have been disproportion- .ately enlarged in FIG. 1. The target electrode assembly 5 includes a metal backing plate 7 having a layer 8 of dielectric material arranged on the side thereof facing ythe electron gun assembly 3 and with a metal grid structure 9 arranged on the side of the dielectric layer 8 remote 11, as is well known in the art.

It will be readily seen that the electron beam 10 has a finite diameter and further that it does not have normal incidence to the target electrode assembly 5 except at the center even if a collimating lens is used. Sincethe grid structure 9 has appreciable thickness, it is readily seen that the beam 10 will be shaded by the grid structure 9 adjacent the outer edges of the target 5, as clearly shown It is further seen that the resolution is restricted by the diameter of the beam 10. It is also apparent that the beam 10 will be properly focused adjacent the center of the target electrode 5 only and vwill be increasingly out of focus as it approaches the outer edges due to geometrical and deflection defocusing.

Referring now to FIG. 2, in which like elements are indicated by like reference numerals, it will be seen that I have provided a bowl-shaped target electrode 12, preferably spherical in configuration, with the locus of its radious of curvature R located approximately at the center of deflection 13 of beam 10. Here it is seen that the metal backing plate 14 is bowl-shaped with the dielectric layer 15 disposed on the inner surface of the bowl 14 and with the grid structure 16 similarly arranged on the side of the dielectric layer 15 remote from the metal backing plate 14` It will now be seen that the electron beam 10 has normal incidence with all points on the target electrode and thus that shading previously encountered with flat targets due to lack of normal incidence of the beam is eliminated. It will further be seen that with the diameter D of the envelope 2 of the tube of FlG. 2 the same as the diameter of the envelope 2 of the tube of FIG. l, the target electrode being bowl-shaped in configuration will have a greater area than the flat target electrode 5 of FIG. 1. Thus, it is possible to obtain better resolution. Conversely, any cross-talk encountered in the arrangement of FIG. l may be reduced by incorporating my improved bowl-shaped target electrode of FIG. 2, without reducing resolution. It is possible to increase the diameter of the curved target over that of a at target because it is now possible to assure normal incidence of the electron beam. It will also be readily apparent that the electron beam will be properly focused at all points on the target electrode and not merely at the center as is the case of the flat target electrode of FIG. 1.

Referring now to FIG. 3, there is shown a barrier grid storage tube having an enclosing envelope 17 with a conventional electron gun assembly 18 positioned therein adjacent end 19. Electron gun assembly 18, which may include cathode, control grid, and accelerating elements, as is Well known in the art, is provided with a plurality of external leads 20 for connecting these elements to appropriate sources of voltage. Vertical and horizontal deflection unit 21 is positioned within envelope 17 in front of the electron gun assembly 18 and is adapted to be connected to suitable vertical and horizontal deflecting signals by leads 22 and 23; it will be readily understood that external magnetic deflecting coils or conventional electrostatic plates may be employed for dellecting the electron beam 24 provided by the electron gun assembly 18 instead of the internal electrostatic deflecting unit 21 as shown in FIG. 3.

A shield electrode 25 is positioned within an envelope 17 in front of the detiecting element 21 and is adapted to be connected to a suitable source of voltage, e.g., minus 100 (-100) volts by lead 26. A secondary emission collecting electrode 27 is positioned Within envelope 17 in front of the shield electrode 25 and is adapted to be connected to a suitable external source of voltage by lead 28. Secondary emission accelerating electrodes 29 andA 30 are located between collecting electrode 27 and the irnproved target electrode 31 of my invention and are adapted respectively to be connected to suitable external sources of voltage, such as plus 100 (+100) volts and plus 200 (+200) volts by leads 32 and 33. The target electrode 31 is preferably spherical shaped having the locus of its radius of curvature located approximately adjacent the point of deflection 34 of the beam 24 and includes spherical metal backing plate 35 and spherical dielectric end grid elements generally identified as 36 disposed on the side of the metal backing plate 35 toward the electron gun assembly 18 for scanning by electron beam 24. The metal backing plate 35 of the target electrode 31 is adapted to be connected to a suitable source of voltage, such as plus or minus 50 (150) volts, by lead 37 and is also adapted to be connected to au output circuit, as is well-known in the art.

In an actual barrier grid storage tube constructed in accordance with FIG. 3, target electrode 31 had a diameter of 41/2 inches and its radius of curvature was also 41/2 inches. The dielectric layer was formed of glass .005 inch thick fused to the inner surface of the spherical metal backing plate 35, as described in my copending application Serial No. 666,969, filed June 20, 1957, and assigned to the assignee of the present application. The grid structure was a Z50-mesh nickel screen .0015 inch thick. Such a screen could be fused to the surface of the dielectric layer remote from the metal backing plate 35 in the manner of my aforesaid application Serial No. 666,969.

In the method of making the improved target electrode of this invention, a blank of relatively thin metal is cut to proper size for forming the bowl. The bowl may be formed of suitable nonmagnetic metals such as copper, nickel, or stainless steel; however, I have found that Inconel is preferred because of its good machining qualities, and further, since it is nonrnagnetic and its expansion characteristics are approximately matched to the expansion characteristics of the glass dielectric layer. The blank is rst degreased and then annealed in an inert atmosphere; I have annealed the blanks in dry hydrogen at 980 C. for twenty (20) minutes. The blank is then cooled, preferably with the dry hydrogen still flowing until the metal is returned to room temperature. In the event that metals other than Inconel are used, it is to be readily understood that annealing at a different temperature for a different period of time may ybe necessary in order to obtain the dead-soft anneal desired.

'Ille annealed metal blanks are then drawn in a conventional die set to approximately the radius of curvature desired. The die set may require some final shaping to obtain the correct curvature of the bowl since the spn'ngback in the material must be taken into consideration. After the bowl has been initially formed, it is again thoroughly degreased and returned to the furnace for another annealing in an inert atmosphere. The blank is then annealed following the same schedule as the initial anneal and as soon as the annealing is completed, the bowl is replaced in the die set and restruck. The annealing and forming steps are continued until the bowl no longer changes its curvature during annealing as determined by careful measurement with a spherometer before and after annealing; I -have found it necessary to repeat the annealing and forming cycle for from four to six times before the bowl becomes sufficiently stabilized.

After the bowl has been formed and stabilized, I have found it desirable to grind its interior surface utilizing conventional optical grinding equipment. I have carried on this grinding in two steps, first grinding with a fairly coarse grit aluminum oxide, e.g., 180, until the bowl is practically to its final shape, and then grinding with a much finer grit aluminum oxide, e.g., 225, until the bowl has its final shape. The shape of the bowl should be carefully checked with a spherometer during the entire `grinding process in order to be sure that the grinding is proceeding properly and great care must be used during the grinding in order to insure that no dis- -tortion takes place in the bowl due to excessive pressure on the grinding tools. It will be readily understood that other grinding compounds may be found more advantageous with other metals.

Following the grinding operation, the bowl is washed, care being taken to insure that the ground inner surface is not scratched or the bowl deformed in any way. I have found that a soft bristle brush with a commercially available detergent washing powder is satisfactory for this cleaning step. Following washing with detergent, the bowl is finally rinsed in tap water and then distilled water, the parts then being dried in an air oven at about C.

A dielectric layer is then deposited on the inner sur- `face of the bowl-shaped metal backing plate, preferably in accordance with the process described in my aforesaid application Serial No. 666,969 and a fine mesh screen, preferably formed in accordance with my aforesaid continuation-in-part application Serial No. 733,250 is positioned on to the surface of the dielectric layer, preferably in the manner described in my aforesaid application Serial No. 666,969.

lt will now be readily apparent that I have provided an improved target electrode for a barrier grid storage tube, and an improved method of fabricating such a target electrode, this target electrode permitting greater resolution for the same tube diameter than that previously provided by at target electrodes, permitting the use of a larger diameter target than has been the case with hat targets, eliminating beam shading caused by the thickness of the grid structure, and providing more accurate reading-out by virtue of the proper focusing of the beam at all points on the target; my invention therefore results in a barrier grid storage tube having either better resolution or less crosstalk or both, features which are now highly desirable in computer technology.

While the preferred embodiment of this invention incorporates a glass dielectric layer fused to the bowlshaped metal backing plate and a bowl-shaped grid structure likewise fused to the glass dielectric layer as more fully described and illustrated in my aforesaid co-pending applications, it will be readily understood that other dielectric materials, such as aluminum oxide imbedded in porcelain enamel, may be employed and that the grid structure may be mechanically held in assembled relation or secured to the dielectric layer by means of a suitable adhesive. It will further be understood that the barrier grid storage tube structure shown in the specific example of FIG. 3, aside from the bowl-shaped target electrode assembly, is shown for illustrative purposes only and that other well-known types of barrier grid storage tube construction may be equally advantageously employed.

While I have described above the principles of my invention in connection with specilic apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

l. The method of making a target electrode for a barrier grid storage tube comprising the steps of: annealing a metal blank; drawing a bowl from said blank; annealing said bowl; repeating said drawing and annealing steps until said bowl does not change shape during annealing; placing a layer of dielectric material on the inner surface of said bowl; forming a metal screen into a bowl shape; and placing said screen within said metal bowl in contact with the outer surface of said dielectric a bowl shape; and placing said screen within said metal bowl in contact with the material layer.

3. The method of making a target electrode for a barrier grid storage tube comprisingthe steps of: forming a bowl from a metal plate; optically grinding the interior surface of said bowl; placing a layer of dielectric material on the inner surface of said bowl; forming a metal screen into a bowl shape; and placing said screen within said metal bowl in contact with the outer surface of said dielectric material layer.

4. The method of making a target electrode for a barrier grid storage tube comprising the steps of: anneal ing a metal blank; drawing a bowl from said blank; annealing said bowl; repeating said drawing and annealing steps until said bowl does not change shape during anhealing; optically grinding the interior surface of said bowl; placing a layer of dielectric material on the inner surface of said bowl; forming a metal screen into bowl shape; and placing said screen within said metal bowl in contact with the outer surface of said dielectric material layer.

outer surface of said dielectric References Cited in the file of this patent UNITED STATES PATENTS Epstein et al Dec. 24, 1957 

